Is the Bosch water pump impeller plastic? If so take a few min of your time and remove it and inspect it. I do the same thing you did and purchased a water pump and Tstat from pep boys. The pump self destructed in less than 100 miles and I almost overheated. I sent it back to Bosch and they paid for the repairs to my vehicle because it was a defective part. I can't get into many details because I signed a document not to disclose much info. Take it out and report back